1. The Field of The Invention
The present invention relates to a process for the preparation of 3-phenoxybenzylalcohol. More particularly, the invention relates to a process by which 3-phenoxybenzylalcohol is prepared from 3-phenoxytoluene.
2. The Prior Art
3-Phenoxybenzylalcohol (mPBL) is an important intermediate in the synthesis of pyrethroid insecticides. However, because of the very high purity required for this intermediate, many of the possible preparation methods known in the art do not lead to industrially useful products.
The halogenation of 3-phenoxytoluene (mPHT) and the subsequent conversion of the resulting mixture of benzyl- and benzal-halides into mPBL or 3-phenoxybenzaldehyde (mPBA) provides a product that is contaminated as the result of the halogenation of the aromatic ring. These contaminants cannot be removed by industrially applicable and useful processes. For instance, the chlorination of the methyl group of mPHT leads to substantial amounts of ring-chlorinated contaminants.
According to German Patent Application 2402457, mPHT is chlorinated using chlorine and PCl.sub.3 at temperature of 250.degree. C., to obtain a mixture of 3-phenoxybenzylchloride (mPHT-Cl) (62.3%) and 3-phenoxybenzalchloride (mPHT-Cl.sub.2) (16.3%). This mixture is refluxed with sodium acetate in acetic acid to give a mixture containing mPHT (63%), 3-phenoxybenzylacetate (14.5%) and mPBA (16.1%). On treatment with sodium borohydrate in alcoholic sodium hydroxide, this mixture gives mPBL in 80% yield (relative to the converted starting material).
According to German Patent 2707232, mPHT is chlorinated under 125W Hg lamp to obtain a mixture of (38.8%) mPHT-Cl, (53.4%) mPHT-Cl.sub.2, (4.6%) 3-phenoxybenzotrichloride and (3.2%) by-products. The mixture is treated with sodium formate in formic acid to give 3-phenoxybenzylformate and mPBA. The ester is hydrolized with sodium hydroxide to give mPBL.
German Patent 2850180 teaches a process in which the product after chlorination, containing (46.9%) mPHT-Cl, (3.6%) mPHT-Cl.sub.2, (46.7%) mPHT and (0.7%) ring chlorinated products, is hydrolyzed with aqueous sodium hydroxide at 180.degree. C. to give a mixture containing (44.9%) mPBL, (4.6%) mPBA, (48.9%) mPHT, (0.2%) mPHT-Cl and (0.6%) ring chlorinated products. This mixture is mixed with aqueous sulfuric acid and toluene and oxidized with sodiumbichromate to give mPBA.
In German Patent 2850179, the chlorination products of mPHT, namely (53.4%) mPHT-Cl, (9.4%) mPHT-Cl.sub.2, accompanied with (32.4%) mPHT and (4.7%) unknown components, were autoclaved with magnesium oxide and water for 3 hours at 180.degree. C., to give (86.4%) mPBL (based on mPHT-Cl).
Japanese Patent 81166142 describes a process in which the hydrolysis was performed on a mixture containing mPHT-Cl and mPHT-Cl.sub.2 by autoclaving with the carbonate or bicarbonate of sodium, potassium or calcium in water. According to this patent the reaction takes place at temperatures between 130.degree. and 250.degree. C., and gives a mixture of mPBL and mPBA.
In another Japanese Patent, JP 81166131, a similar chlorides mixture is hydrolized for 2 hours at 150.degree. C. (5 atm), to give mPBL and mPBA.
Attempts to brominate mPHT with elemental bromine leads to similar problems. Therefore, brominating agents, e.g. N-bromosuccinimide and N-bromoacetamide, have been suggested, e.g., in German Patent 2810305. Recently, an improvement in the art has been reported, wherein a mixture of 3-phenoxybenzylbromide (mPHT-Br) and 3-phenoxybenzalbromide (mPHT-Br.sub.2) were produced without any substantial ring bromination taking place. This process, described in GB 2175895, operates under conditions at which the mPHT is converted almost completely into mixtures of mPHT-Br/mPHT-Br.sub.2, alleviating the need to recycle the starting material. However, it is necessary to further react the mixtures of mPHT-Br/mPHT-Br.sub.2 in order to convert them into mPBL or mPBA, respectively.
If it is desired to prepare mPBA, this can be achieved from the abovementioned mixture in a single reaction step. Preparation of mPBL, however, can be effected only through two additional reaction steps.
It is therefore clear that it would be desirable to provide a simple process for manufacturing 3-phenoxybenzylalcohol with high purity and in high yield.